1. Field of the Invention
The present invention generally relates to transient optical state change security materials reactive to a wavelength of about 630 nm to about 660 nm, in particular to wavelengths produced by DVD optical readers. Such materials may be used by directed application to optical medium to effectuate copy-protection. More specifically, the materials may be used to manufacture optically readable digital storage medium that protects the information stored thereon from being copied using conventional optical medium readers, but permits reading of the information from the digital storage media by the same readers.
2. Description of the Related Art
Data is stored on optical media in the form of optical deformations or marks placed at discrete locations in one or more layers of the medium. Such deformations or marks effectuate changes in light reflectivity. To read the data on an optical medium, an optical medium player or reader is used. An optical medium player or reader conventionally shines a small spot of laser light, the “readout” spot, through the disc substrate onto the data layer containing such optical deformations or marks as the medium or laser head rotates. Two common types of optical media are the CD disc, providing a maximum storage space of about 650 megabytes of data on a single-side (SS), single-layer (SL) disc, and the DVD disc providing about 4.37 GB (1GB=231 bytes) on a single-sided (SS), single-layer (SL) disc. The ECMA Technical Committee TC31 was established in 1984 for the standardization of Optical Discs and Optical Disc Cartridges, making contributions to ISO/IEC SC23 with respect to International Standards.
The vast majority of commercially-available software, video, audio, and entertainment pieces available today are recorded in read-only optical format. One reason for this is that data replication onto read-only optical formats is significantly cheaper than data replication onto writable and rewritable optical formats. Another reason is that read-only formats are less problematic from a reading reliability standpoint. For example, some CD readers/players have trouble reading CD-R media, which has a lower reflectivity, and thus requires a higher-powered reading laser, or one that is better “tuned” to a specific wavelength.
In conventional “read-only” type optical media (e.g., “CD-ROM”), data is generally encoded by a series of pits and lands that are metallized. A readout spot directed from the non-metallized side is reflected in a manner that the light of readout spot is reflected back into a photosensor in the reader. When referenced from the laser reading side, pits are technically referred to as bumps. The transitions between pits and lands, and the timing in between such transitions, represent channel bits. Thus the pit and lands in themselves are not representations of a sequence of zeros or ones. Typically, in CDs 14 channel bits make up a data symbol that translates to an 8 bit data value, in a process referred to as 8 to 14 modulation (EFM). DVD uses a modified version of EFM, known as EFM+ to convert 8-bit data directly into 16 channel bits. The NRZI (non-return to zero inverted) waveform representation is used to interpret the binary sequence on the disc.
Microscopic pits formed in the surface of the plastic medium are arranged in tracks, conventionally spaced radially from the center hub in a spiral track originating at the medium center hub and ending toward the medium's outer rim. The pitted side of the medium is conventionally coated with a reflectance layer such as a thin layer of aluminum or gold. The “pits” as seen from the metallized side, are also referred to “bumps” when referencing view from the laser-read side. A lacquer layer is typically coated on the pit side as a protective layer.
The intensity of the light reflected from a read-only medium's surface measured by an optical medium player or reader varies according to the presence or absence of pits along the information track. As defect-induced errors may interfere with read, all optical discs employ error management strategies to eliminate the effect of such errors.
The optical reader, such as the CD or DVD reader, has the job of finding and reading the data stored as bumps on the disc. In a conventional player a drive motor spins the disc. A laser and lens system focus light on the bumps, and an optical pickup head (PUH) receives reflected light. A tracking mechanism moves the laser assembly so that the laser's beam can follow the spiral track, conventionally moving the laser outward from the center as the disc is played. As the laser moves outward from the center of the disc, the bumps move past the laser faster, as the speed of the bumps is equal to the radius times the speed at which the disc is revolving (rpm). A spindle motor is conventionally employed to slow the speed of the disc when the laser is reading further and further out from the center of the disc permitting the laser to read at a constant speed, such that the data is read from the disc at a constant speed.
The semiconductor laser utilized, the spread of its wavelength, and its operational temperature affect the wavelength read by the pick up head (PUH) of the reader. DVD readers presently utilize lasers that produce a wavelength of about 630 to about 660 nm, with standard DVD readers measuring a wavelength of 650±5 nm and standard DVD-R readers measuring a wavelength of 650 +10/−5 nm. As would be understood by one of skill in the art, the PUHs can detect only those reflected beams that fall within a certain angular deviation from the incident beam. For example, a typical DVD-R requires that the radial deviation be no more than ±0.80° and tangential deviation no more than ±0.30°.
Optical media of all types have greatly reduced the manufacturing costs involved in selling content such as software, video and audio works, and games, due to their small size and the relatively inexpensive amount of resources involved in their production. They have also unfortunately improved the economics of the pirate, and in some media, such as video and audio, have permitted significantly better pirated-copies to be sold to the general public than permitted with other data storage media. Media distributors report the loss of billions of dollars of potential sales due to high quality copies.
Typically, a pirate makes an optical master by extracting logic data from the optical medium, copying it onto a magnetic tape, and setting the tape on a mastering apparatus. Pirates also sometimes use CD or DVD recordable medium duplicator equipment to make copies of a distributed medium, which duplicated copies can be sold directly or used as pre-masters for creating a new glass master for replication. Hundreds of thousands of pirated optical media can be pressed from a single master with no degradation in the quality of the information stored on the optical media. As consumer demand for optical media remains high, and because such medium is easily reproduced at a low cost, counterfeiting has become prevalent.
WO 02/03386 A2, which asserts common inventors to the present application, discloses methods for preventing copying of data from an optical storage media by detecting optical dis-uniformities or changes on the disc, and/or changes in readout signal upon re-reading of a particular area on the optical storage medium, in particular those caused by light-sensitive materials, such as dyes, which may affect the readout wavelength by absorbing, reflecting, refracting or otherwise affecting the incident beam. Software control may be used to deny access to content if the dis-uniformity or change in read signal is not detected at the position on the disc wherein the dis-uniformity or change is anticipated. The disclosure of WO 02/03386 A2 is incorporated herein in its entirety by reference.
A preferred embodiment described in publication WO 02/03386 A2 comprises light-sensitive materials are optically-changeable security materials that are positioned upon the optical disc in a manner that they do not adversely affect the data-read of the readout signal in one optical state but upon exposure to the wavelength of the optical reader incident beam covert to a second optical state, preferably in a time-delayed fashion, that does affect the data-read of the readout signal. In a preferred embodiment described in WO 02/03386 A2, the optically-changeable security material only transiently changes optical state and its optical state reverts over time.
It has been discovered by the present inventors that the optimal characteristics for such preferred transient optically-changeable security materials described in publication WO 02/03386 A2 depend upon a number of factors, including, the characteristics of the incident beam generated by the laser reader used (such as the beam intensity and wavelength), the particular materials used to fabricate the optical disc in particular with respect to the optical characteristics of such materials with respect to the reading beam (such as refractive index and birefringence), the particular formatting of the disc (such as pit depth), where the optically-changeable security material is positioned on or within the disc (e.g., on the surface versus in a layer of the disc/in the data section of the disc versus), the optical characteristics of other materials that may be introduced to effectuate incorporation of the optically-changeable security material onto or into the disc, the characteristics of the pickup head (PUH) of the optical reader in particular with respect to readout wavelength and angle of deviation permitted for pickup of reflected light emanating from the incident beam, the reading characteristics of the optical reader system in particular related to scan velocity, the time for re-scan, and rotational speed of the disc. For example, the material should not change state too quickly so as not to allow the PUH to observe both states. On the other hand, it should not change state too slowly so as to eventuate in a disc that would take non-commercially acceptable times for validation of the disc and read.
An optimal transient optical state change security material should be thermally and photochemically stable under conditions of optical use and at ambient conditions for a significant period of time. It should be soluble in a matrix that comprises the disc, or that can be adheredly-applied to the disc. An optimal transient optical state change security material should revert to its state without the need for extraneous inputs of energy, and should demonstrate a change in optical state at the incident wavelength of the reader.
There is a need for optical state change security materials that may be employed in a manner described in WO 02/03386 A2 to effectuate copy-protection of optical discs, in particular DVDs, that conform to ISO/IEC standards when read by their respective ISO/IEC standardized readers. In particular there is a need for identifying materials that may be used in such copy protection methodologies without requiring modification to optical medium readers.